Harrat Rahat is the largest volcanic field in Saudi Arabia and has been active from ∼10 Ma to the present day. Due to its proximity to population centers, recent eruptions at Harrat Rahat— the Medinah lava flows (2.5 Ma), is poorly understood. In this study, we collected, dated and geochemically analyzed lavas from Harrat Rahat, primarily targeting the under-sampled Shawahit unit. We obtained dates of between 9.4 and 2.7 Ma using 40Ar/39Ar analyses of 23 Shawahit samples. Over the lifetime of Harrat Rahat, we observe a geochemical transition from predominantly subalkalic to alkalic eruptions coupled with a counter-intuitive decrease in incompatible element concentrations. We attribute these changes to a decrease in melt productivity and a reduction in contamination by enriched lithospheric melts, respectively. Thermobarometric analysis of basalts from Harrat Rahat indicates that they were generated by melting of asthenospheric mantle with a potential temperature of ∼ 1456+50/-32 ◦C beneath lithosphere that is 50–60 km thick. These results indicate that volcanic activity at Harrat Rahat was initiated by the arrival of a mantle plume beneath lithosphere thinned by a combination of rifting of the Red Sea and thermal erosion. Furthermore, we propose that this plume, either acting alone or in combination with a number of other plumes, is responsible for the formation of the Arabian swell, as well as much of the Neogene-recent intraplate volcanic activity observed across western Arabia. Our conclusions are consistent with a wide range of geochemical, seismologic, gravimetric, thermochronologic and geomorphic observations.
|Original language||English (US)|
|State||Published - Mar 23 2023|
Bibliographical noteKAUST Repository Item: Exported on 2023-04-05
Acknowledgements: We thank G. Fitton and A. Polat for their review and editorial handling, respectively. We thank V. Camp, J. Day, S. Gupta, F. McNab, M. Mai, N. Odling, J. Roobol and J. Ruch for their help. PB acknowledges support by Shell Global and National Science Foundation Award (EAR-5329212). GR thanks the Royal Society (RG160020), NERC (IP-1635–0516; NE/T012501/1), Leverhulme Trust (RPG-2019–073), King Abdullah University of Science and Technology and the Saudi Geological Survey for their support.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.